数据结构与算法

1. Two Pointers
2. Binary Tree BFS
3. Topological Sort
4. Binary Tree DFS
5. Top K Elements
6. Modified Binary Search
7. Subset
8. Sliding Window

时间与空间复杂度

What is Big O Notation

Time complexity = a way of showing the runtime if a fuction increases as the size of the input increases

Space complexity = a way of showing the memory if a function increases as the size of the input

Types of Big O Notation

• Constant time (0次方程) O(1): 不用循环
• Linear tim e (1次方程) O(n): 循环1层
• Quadratic time (2次方程) O(n^2): 循环2层
• O(N!), O(2N * N), O(2N/2 * N), O(N* log N)…

How to determine O(n)

1. find the fastest growing term
2. take out the coefficient (系数)